In recent years, the progress of ink-jet technology has been remarkable, and as a result, ink-jet image quality has been called photographic image quality due to enhancement of printer technology, ink technology and specific recording medium technology. In accordance with enhancement of image quality, ink-jet image storage stability has been favorably compared to conventional photography. In many cases of dye ink, pointed out as drawbacks are deterioration of ink-jet images accompanied with transfer of coloring materials as well as poor water resistance and poor anti-bleeding property, in addition to deterioration accompanied with chemical reactions specific to coloring materials such as light stability and oxidizing gas resistance.
On the other hand, to improve storage stability of dye ink images, usage of pigment ink has been proposed by many knowledgeable in the art. However, in the case of pigment ink, it may not be preferable due to the possibility of not achieving enough glossiness as with silver halide photography, or exhibiting metallic luster known as bronzing. Further, in the present situation, sufficient image storage stability cannot be achieved by only employing pigment ink.
Recognizing the foregoing problems, to enhance image storage stability of ink-jet recording images, many proposals have been disclosed. For example, as an ink-jet recording medium, an accomplishment is described in Japanese Patent Application Publication Nos. 59-22238 1, 4-21446, 10-315448, 11-5362 and 11-192775 (hereinafter, referred to as JP-A Nos.) to improve water resistance and weather resistance and to provide image glossiness during formation of a high polymer protective coating, which is prepared with a layer comprising thermoplastic organic polymer particles provided that the outermost layer of the recording medium, and the thermoplastic organic polymer particles are melted to form a film layer after image recording.
However, in the technologies described in the foregoing official publications, there are some insufficient points in some characteristic criteria. Firstly, scratch resistance is insufficient. The images described in the above publications exhibit preferable image quality, due to enhanced glossiness with formation of a resin layer, but on the other hand, the surface is easily scratched and the scratches tend to be highly visible, which calls for improvement. Secondly, print cracking resistance is also not adequate. Specifically, the problem is that images suffer cracking in portion or the total area in cases when images are stored for relatively long periods or are exposed to high temperature and humidity conditions. Thirdly, scratch resistance under high humidity is insufficient. This is a phenomenon in which images or layers can be easily peeled off by simple finger rubbing when wet. For example, when images wetted by spilled water or coffee, or by rain when viewed outdoors, the images or the layers may be peeled off when wiped. When images are printed with pigment ink, which printing recently has spread rapidly, these problems are more serious. In addition, when printed with pigment ink, pigment does not permeate, or only slightly permeates into the deeper portions of the recording medium as is the case with dye ink. Accordingly, expression of glossiness may be insufficient, or the bronzing phenomenon may result. It is desired to overcome these problems.
On the other hand, a method of a pressurizing treatment of a layer containing thermoplastic organic polymer particles after image recording is proposed (for example, in Patent Document 1). However, considering the results of the Examples, there is no layer thickness change between before and after the pressurizing treatment, and thus, the need for compressing the layer thickness cannot be specifically identified.
Further, a method to make a layer non-porous by a heating process, in which a layer comprising a thermoplastic resin at a void ratio of 15-40% is proposed (for example, in Patent Document 2). However, in this method, only a heating process is mentioned, not compression of the layer thickness by providing a pressurizing treatment. And the degree of compressing the surface layer is not described at all.
Further, methods to add a specific amount of an inorganic pigment to a thermoplastic resin containing layer are described (for example, in Patent Documents 3-5). However, not described in any of these methods, is compression of the layer thickness with a pressurizing treatment nor the degree of the surface layer compression.
Patent Document 1: JP-A 7-237348
Patent Document 2: JP-A 11-5362 (claims)
Patent Document 3: JP-A 2002-234256 (claims)
Patent Document 4: JP-A 2002-234246 (claims)
Patent Document 5: JP-A 2002-234248 (claims)